Process for the preparation of foamable styrene polymers

ABSTRACT

A PROCESS FOR PREPARING FOAMABLE STYRENE POLYMER BEADS CONTAINING BLOWING AGENTS WITH A PARTICULARLY FAVOURABLE, NARROW GRAIN SIZE DISTRIBUTION. THIS NOVEL PROCESS COMPRISES THE USE OF COPOLYMERS OF N-VINYL-N-ALKYL ACETAMIDE HAVING FROM 1 TO 4 CARBON ATOMS IN THE ALKYL GROUP WITH AN ESTER OF ACRYLIC, METHACRYLIC, MALEIC OF FUMARIC ACID WITH AN ALIPHATIC ALCOHOL HAVING A LINEAR OR BRANCHED CHAIN AND CONTAINING FROM 6 TO 18 CARBON ATOMS, AS PROTECTIVE COLLOID IN THE HOMO- OR COPOLYMERIZATION OF STYRENE IN AN AQUEOUS SUSPENSION IN THE PRESENCE OF A BLOWING AGENT.

United States Patent PROCESS FOR THE PREPARATION OF FOAM- ABLE STYRENE POLYMERS Horst Jastrow, Niederhochstadt, Michael Lederer, Falkenstein, Taunus, and Elmar Heiskel, Langen, Germany, assignors to Farbwerke Hoechst Aktiengesellschaft vormals Meister Lucius & Bruning, Frankfurt am Main, Germany No Drawing. Filed Nov. 15, 1971, Ser. No. 198,943 Claims priority, application Germany, Nov. 16, 1970, P 20 56 217.8 Int. Cl. C081? 47/10; C083 1/26 US. Cl. 260-2.5 B 6 Claims ABSTRACT OF THE DISCLOSURE The present invention relates to a process for the preparation of foamable styrene polymers.

The polymerization of styrene in the presence of blowing agents in order to give foamable polystyrene is effected in an aqueous suspension. Particularly suitable from the technical point of view is a bead polymer containing blowing agents, which polymer is obtained with a narrow grain size distribution, the diameter of the grains being in the range of from 0.3 to 1.2 mm.

It has ben proposed in German Auslegeschrift No. 1,273,199 to polymerize styrene in the presence of from 0.1 to 1% of a water-soluble organic protective colloid, such as gelatine, starch, poly-N-vinyl pyrrolidone, polyvinyl alcohol, oxethyl cellulose or carboxymethyl cellulose, in which process the total or the principal amount of the protective colloid is added before the rate of polymerization has been reached at which the polymer particles which have flowed together no longer separate (Japanese Pat. No. 20 456/68, German Auslegeschrift No. 1,150,527, British Pat. No. 1,094,315). The moment which is suitable for the addition has to be determined by way of sampling during polymerization.

Furthermore, German Auslegeschrift No. 1,150,527 proposes to prepare bead polymers having a narrow grain size distribution and containing blowing agents by way of suspension polymerization of styrene in the presence of sulfonated vinyl aromatic polymers containing from 0.5 to 1 sulfonic acid group per monomer unit. In this process use is made of 1.5%, calculated on water, or 2%, calculated on styrene, of resin sulf-onates with good swelling properties which are, however, difficult to prepare.

It has also been proposed to obtain a' narrow grain size distribution in the suspension polymerization by using a combination of suspension auxiliary agents consisting of about 0.4% (calculated on the monomer) of water-solu; ble cellulose derivatives and a small amount of N-vinylpyrrolidone-acrylic acid copolymers. However, this mixed system is only applicable in the range of a large phase ratio of styrene to water 1.

It is more advantageous, however, to use a uniform system instead of a mixture. r

Furthermore, German Ofienlegungsschrift No. 1,595,- 478 describes the adjustment of the grain size distribution 3,758,425 Patented Sept. 11, 1973 by using the combination of from 0.2 to 1% of tricalcium phosphate (TCP) and from 0.01 to 2% of wetting agent. This process is particularly disadvantageous owing to the preparation of a thioxotropic TCP paste of a determined consistency prior to polymerization, and also because of the fact that a considerable amount of surface-active substances has to be added. In this process the waste water problem is particularly critical.

Belgian Pat. No. 641,634 describes the use of poly-N- vinyl-methyl acetamide in a large phase ratio for the suspension polymerization of styrene. In the polymerization with a small phase ratio, i.e. styrene/water 1 (weight ratio), difficulties are caused by the formation of a coatmg.

The use of copolymers of N-vinyl-N-methyl acetamide with from 1 to 9% of octyl acrylate having a low K value resulted in lentilor rice-shaped polymers and/ or a strong wall coating.

It has now been found that the polymerization of styrene or of mixtures of styrene with up to 10% by weight of its alkyl derivatives or its derivatives having been halogenated in the nucleus, optionally in admixture with up to- 10% by weight, calculated on the total amount of monomers, of esters of acrylic or methacrylic acid with aliphatic alcohols, acrylonitrile, vinyl chloride, vinyl esters of aliphatic carboxylic acids, and vinyl polysiloxanes in an aqueous suspension, with the aid of common initiators and with the addition of a blowing agent and a protective colloid, leads to a particularly favourable grain size distribution, if as protective colloid there is used a copolymer of'from 98 to 99.5% by weight of N-vinyl-N-alkyl acetamide having from 1 to 4 carbon atoms in the alkyl group, preferably N-vinyl-N-methyl acetamide, and from 2 to 0.5% by weight of an ester of acrylic, methacrylic, maleic or fumaric acid with an aliphatic alcohol having a linear or branched chain and containing from 6 to 18 carbon atoms, preferably 2-ethylhexyl-acrylate, with a K value according to Fickentscher, measured with a 1% solution in methanol at 20 C., of from to 120, preferably from to 100, in an amount offrom 0.02 to 0.08% by weight, preferably from 0.03 to 0.05% by weight, calculated on the monomer and/ or the monomer mixture.

By means of varying the amount of protective colloid, it is possible to adjust the range of the particle size within 300 and 2,500 without a considerable proportion of technically useless fractions having a particle size of more than 2,500 and less than 300 4 being formed.

Particularly suitable are copolymers having a K value according to Fickentscher of from 70 to 120, preferably from 80 tov 100, measured with a 1% solution in methanol at 20 C.; it is also possible to use copolymers having a higher molecular weight, however, this does usually not have any. special advantages.

The preparation of the copolymers used in accordance wtih the invention of from 98 to 99.5 by weight of N- vinyl N-alkyl acetamide and from 2 to 0.5% by weight of alkyl acrylate, methacrylate, maleinate or fumarate is effected preferably according to the process described in German Pat. No. 1,246,248.

:Suitable comonomers of N-vinyl-N-alkyl acetamide, besides Z-ethyI-heXyl-acrylate to be used preferably, are, for example, n-hexyl-acryliate, decyl-methacrylate, dodecyl-m'alein'ate, and steary-l fumarate.

It is recommended to carry out the suspension polymerization while using from 0.02 to 0.08% by weight, calculated on the monomer or the monomer mixture, of dispersion agent according to the invention, preferably from 0.03 to 0.05% by weight. A higher concentration of the dispersion agent is not necessary for the reproducible adjustment of a narrow grain size range of between 300;]. and 2,500 1. It is indeed the use of a very small amount of dispersion agent according to the invention, which enables ticular with regard to waste water problems. Besides, it is very advantageous that the grain size range can be adjusted by specific dosage of the dispersion agent at given stirring conditions, so that operations such as sampling do common for polystyrene polymers, such as hydrocarbons, for example, n-pentane, isopentane, cyclopentane, hexane, and petroleum ether fractions, or halogen hydrocarbons, such as CFC13, 'CF CI CH Cl, CH CI separately, or in admixture with one another. The polymerization temnot have to be carried out during polymerization. 5 peratures are in the range of from 40 to 125 C., with The suspension polymerization is advantageously carpressures rising up to 16 atmospheres gage. ried out in a phase ratio of monomers to water 1 Together with the monomer mixture, or together with (weight ratio); less economical phase ratios 1 can natthe propellant, a very small amount l% by weight) urally also be achieved in the polymerization by means of nucleating agent may also be added for pore regulaof this system. Salts may be dissolved in the aqueous tion. For this purpose, use is made of the common brophase, or organic liquids which are miscible with water mine compounds, such as hexa-bromo-cyclo-dodecane, can be added to it. tetrabromo-butane, tris-(dibromo-propyl-phosphate), as The monomers to be Fsed 1in tilt; galynerizatign arg. well as bgommaitled 011%3111618 offlibutadielne an li cllfioririie styrene in an amount 0 at east 0 0 y weig t an compoun s, suc as c oropara ns, po yviny c ori e optionally up to 10% by weight of acrylic esters and/or and post-chlorinated PVC, as well as polysiloxanes and/ methacrylic esters of aliphatic linear or branched alcoor vinyl polysiloxanes, for example those having the conhols, preferably those having from 1 to 8 carbon atoms, stitution indicated above, with regard to the monomers. acrylonitrile, vinyl esters of aliphatic linear or branched Moreover, the suspension polymerization of the invencarboxylic acids, preferably those having from 1 to 12 tion can be used for the preparation of flame-proof stycarbon atoms, vinyl chloride and vinyl polysiloxanes. Up rene polymers. In this process, from 0.1 to 3% by Weight, to 10% by weight of the styrene may be replaced by subcalculated on the polymer, of one or several halogen stituted styrenes such as alkylated styrenes, for example, compounds, as well as a small amount of a synergist, are y Y P Z teffi butyl y styrenes which are added to the monomer or the monomer mixture, prior to halogenated 1n the nucleus, for example, bromo-styrene. the common suspension polymerization As acrylic esters that can be copolymerized with styrene Common halogen compounds used for obtaining fiame there are suitable, for example, ethyl acrylate, hexyl methproofness are for example, hexabrommcyclwdodecane izi i ggfifig z gg; gg'gzgg 'g gfg zgfiz{ k y tetrabromobutane, tris (dibromo propyl phosphate) formate, vinyl acetate, vinyl propionate, vinyl hexoate, or f i f Further addmons 9 1% by commercial mixtures of branched carboxylic acids. As welg ca i on the Poymer may consist of a comvinyl polysiloxanes there may be used those, which are men synerglst m ohder to lmprove.the 9 prepared by means of cohydrolysis of compounds of for example phroxldes h h dlchmyl Peroxlde, formula c12Si(R)(cH:CH2) with compounds of tert.-butyl-perox1de, or of indigold substances or nadicalmula z uua example, 2 3)(CH=CH 5 y l lng substances, such as tetraphenyl-dimethyl-ethane. With 2 a)2, and which contain units of formulae Besides, plasticizers, auxiliaries improving the fluidity, R R optical brighteners, or dyestuffs may be added to the 0 i I and -o-si- 11 monomers The following examples serve to illustrate the inven- H=om 40 tion. and hydroxyl terminal groups, in which R stands for identical or difierent alkyl groups having from 1 to 4 EXAMPLES 7 carbon atoms, and the ratio of I to II is from 1:4 to 1:50. I an enameled vessel, 7 parts by volume of Water and T l r w g t o these polysiloxanes is in the range 83 parts by volume of styrene were heated at 90 C. of from f t 1,000 about 9 under a nitrogen atmosphere, while stirring, together with The chhdlhohs of the ShSPehslh'n polymellhahon h the amount indicated in the following tables of a copolyh hommcfn Ones: In a Pressure vesel Provlded Wlth mer of N-vinyl-N-methyl-acetamide and 1% by Weight of st rrer, a m1xture of water and the monomer or monomer z ethyl hexyl acrylate (calculated on the amount of m xture 1s brou ght to an elevated temperature, together Styrene), having a K value of according to Fickent s g r g z z z s agent and mmator or an mmator sober, and the reaction mixture was initiated by a mix- As initiators there are used, for example, dibenzoyl cqnslstmg by welght of dibenzoyl Peroxide peroxide, azodi-isobutyro-nitrile, and tert.-butyl perace- 1% by welght of tert"butyl'perbenzoate (each caltate in an amount of from 0.1 to 0.5% by weight, calcu- 55 i h on the amount styfehe); after? hours the Inter lated on the monomer or the monomer mixture The nal temperature was mamtamed at C. for 4 hours, polymerization may be started in the presence of from q y P y was Cooledby 4 to 12% by weight of a blowing agent which may, how. weight of a vmylpolysiloxane was added to the monomer ever, be added also when the polymerization is already mixture for .3 P p of P regulation 5 hours after running, preferably at a polymerization rate of from 50 60 the initiation, 9 parts by volume of pentane were pressed to 55%. As blowing agents there may be used those over a sluice into the closed stirring vessel.

TABLE 1 Percent y wt. of Residue on the sieve 1n percent in mm. Example ag g iii R.p.rn 2 5 2.0 1.6 1.0 0.8 0.6 0.4 0.32 0.2

v0.1 0.1 0.2 2.7 3.8 10.4 15. 15.3 12.3 0.06 150 0.2 0.4 6.1 20.2 12.8 13.5 9% 13. 1 .3 8382 i3?) 81% 31. 52:2 53:3 1%? i815 2:4 5:0 2:0 0.04 130 0.5 7.5 25.2 25.5 13.9 13.8 7.0 5.1 0.3 0.04 130 0.5 2.2 22.5 40.8 11.0 10.6 3.0 2.2 0.5 0.04 130 0.4. 2.0 20.2 36.2 11.3 11.2 4.3 4.0 2.0 0.04 130 0.2 2.5 20.2 47.9 11.3 8.4 2.1 1.0 0.3 0.03 -1.5 15.2 I 32.7 49.9 6.6 1.1 0.1 0.1

1 Calculated on styrene.

NorE.Fl.-pr. =with the addition of 600 g. of hexabromo-eyclododecane and 375 g. of di-tert.-butyl peroxide for the preparation ofa flame-proof type. The reproducibility of the grain size adjustment in the range of from 800 to 2,000/ 4 becomes particularly evident in reaction IlllXtlJlGS 4 to TABLE 2 Percent by wt. of Percent dispers by Wt. of K agent I com. value Rpm. .2. 5 2.0 1 6 1.0 0. 8 0. 6 0.5 0. 4 0. 32 0. 2 0. 1

0. 04 85 150 4 X 0. 06 86 150 4 X 0. 04 0.25 95 150 4 X 0, O4 0. 5 84 130 0.3 5. 33. 7 32. 14. 7 8. 7 5. 0 0. 1 0. 04 2. 0 87 150 0. 3 8. 0 29. 2 39. 5 9. 5 9. 3 4. 1 4. 6 1. 4 0. 1 0.05 4. 0 150 Lentils and coating 0, 05 9. 0 150 Lentils and coating 1 Calculated on styrene. 2 2-ethyl-hexyl-acrylate was used as comonomer. 3 Without. 4 Phase separation during polymerization. Wh i l i d i cording to Fickentscher, measured with a 1% solution in 1. In a process for the polymerization of styrene or of mixtures of styrene and up to 10% by weight of its alkyl derivatives or its derivatives having been halogenated in the nucleus, optionally in admixture with up to 10% by weight, calculated on the total amount of monomers, of esters of acrylic or methacrylic acid with aliphatic alcohols, acrylonitrile, vinyl chloride, vinyl esters of aliphatic carboxylic acids, and vinyl polysiloxanes in an aqueous suspension, with the aid of common initiators and with the addition of a blowing agent and a protective colloid, the improvement which comprises adding during the polymerization as protective colloid a copolymer of (a) from 98 to 99.5% by weight of N-vinyl-N- alkyl acetamide having from 1 to 4 carbon atoms in the alkyl groups, and (b) from 2 to 0.5% by weight of an ester of acrylic, methacrylic, maleic or fumaric acid and an aliphatic alcohol having a linear or branched chain and containing from 6 to 18 carbon atoms, having a K value according to Fickentscher, measured with a 1% solution in methanol at 20 C., of from 70 to 120, in an amount of from 0.02 to 0.08% by weight, calculated on the monomer or the monomer mixture.

2. A process as claimed in claim 1, wherein an amount of from 0.03 to 0.05% by Weight, calculated on the monomer or the monomer mixture, of the copolymer constituting the protective colloid is used.

3. A process as claimed in claim 1, wherein the copolymer constituting the protective colloid has a K value acmethanol at 20 C., of from to 100.

4. A process as claimed in claim 1, wherein the N- vinyl-N-alkyl acetamide in the copolymer used as protective colloid is N-vinyl-N-methyl acetamide.

5. A process as claimed in claim 1, wherein a copolymer of N-vinyl-N-alkyl acetamide with 2-ethy1-hexy1- acrylate is used as protective colloid.

6. A process as claimed in claim 1, wherein a copolymer of N-vinyl-N-methyl acetamide with 2-ethyl-hexylacrylate is used as protective colloid.

References Cited UNITED STATES PATENTS 3,001,954 9/1961 Buchholz et a1. 2602.5 B

2,888,410 5/1959 Buchholz 260-25 B 2,983,692 5/1961 DAlelio 2602.5 B

FOREIGN PATENTS 641,634 12/1962 Belgium 26093.5W

MURRAY TILLMAN, Primary Examiner M. FOELAK, Assistant Examiner U.S. Cl. X.R.

26045.7 R, 45.7 P, 85.5 AM, 85.5 XA, 85.5 ES, 85.5 N, 86.3, 86.7, 87.5 R, 88.1 P, 88.2 C, 93.5 W, 827, 881, 884, 885, 886, 898, 899, 901, DIG. 24 

